Some are calling it Winter Storm Enzo (not official) or as the newly renamed Gulf of Mexico maybe we should just call this the Winter Storm “Gulf America”. This winter storm is poised to deliver an uncommon weather event across the southeastern United States, bringing snow and ice from Texas through the Carolinas. This storm, which will impact areas like Houston, New Orleans, and parts of Florida and Georgia, has prompted states to declare emergencies and issue travel warnings. Local governments are preparing road treatments and school closures to mitigate the effects of the storm expected to hit Tuesday into Wednesday.
Which areas in Atlanta will see snow? How much snow is expected?
Areas south of I-20 will have the best chance of accumulating snow. About 1-2 inches of snow are possible over our far southern counties.
In and around metro Atlanta the forecast is tricky because it all depends on how quickly the mid and low levels of the atmosphere can moisten up.
The NWS of Atlanta made a long and detailed post explaining that the city is in the zone of uncertainty for snowfall amounts:
Answering the elephant in the room – why has this been such a difficult weather forecast and why are there still many unknowns 24 to 36 hours out?
This post is going to dive a little into the science and forecast analysis. So, if you’re a weather weenie keep reading, if not well you should still keep reading. When looking at weather models you may be tempted to only look at the reflectivity output or the precipitation type output. That’s great and all BUT it’s even better to take a peek at what the atmosphere looks like in the vertical i.e., model forecast soundings!
The big question we’re asking ourselves right now is how far north can we expect snow to occur? Well for snow we need the atmosphere to be saturated with temperatures below freezing. One way we can get a better look at how dry or saturated the atmosphere is at a specific point is by looking at these model forecast soundings (very much like our weather balloon soundings – these are just at a specific time in the future).
As an example, we’ve chosen a model forecast sounding for here in Peachtree City, with the red line being temperature and the green line being the dewpoint. When these lines come really close together that means our atmosphere is saturated. And, you guessed it, the farther apart they are, means the atmosphere is drier. So, we want the temperatures and dewpoints to be closer together AND below Kreezing. But what happens if drier air is noted near the surface (i.e., towards the bottom part of the sounding) as shown below? Well, the frozen precipitation would fall through the dry air layer and begin to evaporate. The question then becomes, how deep is that dry layer and is it too much dry air for snow to successfully reach the ground?
This is where the headache lies. For this event in particular, many weather models have depicted reflectivity stretching northward reaching locations near the I-20 corridor but showing no precipitation reaching the ground that far north. Essentially what this means is models are struggling with the interaction of frozen precipitation and the layer of dry air. Thus, may be slower to resolve a more saturated atmospheric profile which is why we are seeing the reflectivity but not the precipitation. But this also shows why it’s so important to look at model forecast soundings when doing meteorological analysis, not just one models output.
One final thing to note are the wind barbs on the right of the sounding. Southwesterly winds as depicted below suggest moisture being ushered into the area ahead of the storm system. If enough moisture surges into the area, this may be just enough to saturate the atmosphere, weakening the dry layer and allowing for that snowfall. Given how cold we are anything that falls will stick and lead to impacts.
At this time, we are asking ourselves will there be a window of opportunity in which southwesterly winds usher in enough moisture to weaken the dry layer and allow for snow to reach the surface as far north as I-20 corridor.
If you’ve made it this far – thank you for reading and I hope this provided you with helpful information regarding the difficulty of this particular forecast.
Great stuff! Read more here about snowfall forecasting.